_.any can return incorrect results when native forEach functions are used

[lshearer]

When a native forEach function is present, if _.any is called with a list in which the last item does not pass the truth test it will always return false (even if any other items in the list passed the truth test). The problem is that the native forEach function does not short circuit (return breaker; has no effect on it). Therefore, the return result for the call to _.any will be overwritten by the last item.

Suggested fix:

Replace

            if (result = iterator.call(context, value, index, list)) return breaker;

with

            if (result |= iterator.call(context, value, index, list)) return breaker;

in _.any, resulting in:

    var any = _.some = _.any = function (obj, iterator, context) {
        iterator = iterator || _.identity;
        var result = false;
        if (obj == null) return result;
        if (nativeSome && obj.some === nativeSome) return obj.some(iterator, context);
        each(obj, function (value, index, list) {
            if (result |= iterator.call(context, value, index, list)) return breaker;
        });
        return !!result;
    };

This prevents result from being set to true and then later being overwritten by false.

Edit: because the |= operation returns an integer, to maintain a strictly boolean return type, the return value would need to be !!result

[shinuza]

The is issue exists but the fix is partially incorrect, the original code reads :

if (result = iterator.call(context, value, index, list)) return breaker;

not

if (result == iterator.call(context, value, index, list)) return breaker;

which does override result with whatever the iterator returns if the each doesn't support iteration break.
See pull request #197 for the fix.

[lshearer]

Yes, I mistyped the original code, but my fix is correct. If result is ever set to true, the |= operation will never set it back to false. Your fix also achieves the correct result, but I did it this way because it is slightly more compact.

[shinuza]

Sorry I misread |= as !=, that's why I thought something was wrong with your code. Pull request updated.

[jashkenas]

Already commented this on the pull request -- but this needs to have some test cases added.

[jashkenas]

This should be fixed as of the corresponding pull request.

[jdalton]

I dig this patch/issue... I'm curious under what circumstances did this bug happen (an object passed the has native forEach(), but not some())?

[shinuza]

Would happen if your environment doesn't support neither forEach nor some, and you add forEach manually by extending Array.prototype, then use .any/.some.

[chrisaaaker]

Repeating the question from @jdalton ( but modified ), from 2 years ago, are there any cases when a native forEach is present but a native some is not present, AND the prototype chain has not been user modified to effect this? That is, a browser has implemented the language this way?

[jdalton]

@chrisaaaker It's for when a 3rd-party lib shims one native array method and not another.